svimg is an image preprocessing and lazy loading component for Svelte. It consists of:
- A Svelte preprocessor that automatically resizes your images to multiple resolutions in a
srcset
, creates additional AVIF and WebP versions, and generates blurred placeholder images - A Svelte component that displays the blurred placeholder and automatically lazy loads the proper resolution image when it comes into view
svimg uses native browser lazy loading with a fallback to IntersectionObserver, and automatically calculates the appropriate sizes
attribute. Some other image components do not set a proper sizes
attribute, which can cause the browser to download a much larger resolution image than necessary if you are resizing the image with CSS. svimg will also use a literal width if specified to control image preprocessing and only generate the necessary image files for that width.
Since svimg is an external Svelte component, you'll want to make sure it gets bundled by Svelte during compile by installing it as a dev dependency (or modifying your rollup/webpack config to not treat it as an external).
npm install -D svimg
In rollup.config.js
, add imagePreprocessor
as a preprocessor for rollup-plugin-svelte
:
import { imagePreprocessor } from 'svimg';
export default {
plugins: [
svelte({
preprocess: [
imagePreprocessor({
inputDir: 'public',
outputDir: 'public/g',
webp: true,
avif: true
})
]
})
]
};
If you're using Sapper, add the preprocessor to both the client and the server svelte plugins. Make sure to use the same instance of imagePreprocessor
for both client and server, to avoid redundant double-processing of image files:
import { imagePreprocessor } from 'svimg';
const preprocess = [
imagePreprocessor({
inputDir: 'static',
outputDir: 'static/g',
webp: true,
avif: true
})
];
export default {
client: {
plugins: [
svelte({
preprocess
})
]
},
server: {
plugins: [
svelte({
preprocess
})
]
}
};
<script>
import Image from 'svimg';
</script>
<Image src="images/splash.jpg" />
<Image src="images/avatar.jpg" width="150" alt="Avatar" class="blue-border" quality="85" immediate />
The Image
component will render a blurred placeholder, a srcset with multiple resolutions, a sizes attribute, and sources of type image/avif
with avif images and image/webp
with webp images.
svimg is also exposed as a custom element, which means it can be used independently of Svelte with the <s-image>
tag.
Usage as a custom element expects that the attributes that would normally be filled in by the Svelte preprocessor (srcset
, srcsetavif
, srcsetwebp
, placeholder
) are populated by another method.
Generally, you'd use another tool to create these elements such as rehype-svimg rather than using the custom element directly.
<script>
import 'svimg/dist/s-image';
</script>
<s-image srcset="images/splash-600.jpg 600w, images/splash-1200.jpg 1200w" srcsetavif="images/splash-600.avif 600w, images/splash-1200.avif 1200w" srcsetwebp="images/splash-600.webp 600w, images/splash-1200.webp 1200w" />
Property | Default | |
---|---|---|
src | required | Image url |
alt | Alternate text for the image | |
class | CSS classes to apply to image | |
width | Resize image to specified width in pixels. If not specified, generates images of widths 480, 1024, 1920, and 2560. | |
immediate | false |
Set to true to disable lazy-loading |
blur | 40 |
Amount of blur to apply to placeholder |
quality | sharp default | Quality of the resized images, defaults to sharp's default quality for each image format |
The following properties will be automatically populated by the preprocessor:
Property | |
---|---|
srcset | Responsive images and widths |
srcsetavif | Responsive AVIF images and widths |
srcsetwebp | Responsive WebP images and widths |
placeholder | Blurred placeholder image |
aspectratio | Aspect ratio of image |
Option | Default | |
---|---|---|
inputDir | required | The static asset directory where image urls are retrieved from |
outputDir | required | The output directory where resized image files should be written to. This should usually be a subdirectory within the normal static asset directory |
publicPath | The outputDir relative to the inputDir static asset directory |
The public path that images will be served from. This will be prepended to the src url during preprocessing. The default behavior will work for most use cases, where the outputDir is a subdirectory of the inputDir static asset directory and the site is served from the root of the domain. This can be overridden for more advanced use cases, such as a site served from a subdirectory of the domain or for images served from a separate domain such as a CDN or static asset domain. |
avif | true |
Whether to generate AVIF versions of images in addition to the original image formats |
webp | true |
Whether to generate WebP versions of images in addition to the original image formats |
- Chris Han - Initial work - xiphux
This project is licensed under the ISC License - see the LICENSE.md file for details